Water inrush hazards from the floor strata of longwall workingface are commonly encountered in North China coalfields,which essentially result from the evolution of permeability in the floor rock under complex mining-...Water inrush hazards from the floor strata of longwall workingface are commonly encountered in North China coalfields,which essentially result from the evolution of permeability in the floor rock under complex mining-induced stress conditions.Current research rarely addresses the evolution of rock permeability under such complex stress paths.Describing this evolution using only one stress parameter,such as effective stress,deviatoric stress,axial stress,or confining stress,is highly challenging.In this study,we developed a laboratory loading scheme that simulates mining-induced stress evolution.Hydro-mechanical experiments were conducted to investigate the evolution of rock permeability under mining stress.The mechanism on the change of stress-permeability relationships in mining-disturbed rock is revealed,supporting to the analysis of management strategies for floor water-inrush disasters.The results show that rock permeability evolves through four stages,including rapid decline,gradual fluctuation,sharp increase,and slow attenuation.1–2 permeability surges occurred during mining-stress loading,closely linked to the emergence and reversal of deviatoric stress in magnitude and direction.With the first permeability surge,the deviatoric stress within the mudstone reached approximately 1.7 MPa,whereas that of the sandstone was about 1 MPa.The second permeability surge in the mudstone corresponded to the secondary rotation of the principal stress direction.CT and ultrasonic tests suggested an increase in microcracks in both rocks during the first permeability surge.However,the deviatoric stress-permeability plot before and after mining indicated that the fracture of mudstone sample changed significantly,while that of the sandstone remained unchanged.The permeability surges observed at different stages are interpreted as resulting from shear-induced reopening of pre-existing fractures and the formation of new shear-failure fractures.A stress-permeability model jointly governed by effective mean stress and deviatoric stress was established.Furthermore,two strategies are proposed for the floor water-inrush disasters prevention,(i)timely backfilling to reduce deviatoric stress,(ii)grouting after the first permeability surge.This work provides insights into stress-seepage behavior in rocks under complex stress evolution and offers new perspectives for identifying potential water inrush pathways in the floor strata of coal seam during longwall mining.展开更多
Prediction of permeability changes in surrounding rock induced by engineering disturbances is crucial for mitigating tunnel water inrush accidents.This study investigates the progressive failure characteristics and pe...Prediction of permeability changes in surrounding rock induced by engineering disturbances is crucial for mitigating tunnel water inrush accidents.This study investigates the progressive failure characteristics and permeability evolution of hard and soft rocks subjected to triaxial compression.A series of laboratory tests were conducted at confining pressures ranging from 4 to 20 MPa.Experimental results demonstrate that rock permeability variation with strain shows three distinct stages:an initial decrease,a stage of rapid mutation,and a postpeak increase.The concept of critical permeability barrier strength is introduced,representing the stress level at which continuous fracture formation enables significant seepage.Furthermore,two generalized permeability–stress models are developed for soft and hard rocks.The predicted permeability values obtained from these models align well with the experimental data.These findings offer valuable insights into the hydro-mechanical coupling behavior of rocks,providing a foundation for safe construction practices in underground engineering.展开更多
Enzyme-induced carbonate precipitation(EICP)is a potential ground improvement method that can reduce the permeability of sands.However,the traditional mathematical models are hard to accurately predict the permeabilit...Enzyme-induced carbonate precipitation(EICP)is a potential ground improvement method that can reduce the permeability of sands.However,the traditional mathematical models are hard to accurately predict the permeability of EICP-treated sands.In this study,the mathematical model was established for predicting the permeability of EICP-treated sands based on Kozeny-Carman equation.The effects of calcium carbonate precipitation on the porosity,tortuosity,and specific surface area of the EICP-treated sands were considered in the model.To validate the model,the bio-cemented sand column tests with different grain size distributions(coarse,medium,and fine sands)and treatment numbers(6,8,and 10 times)were conducted.The calcium carbonate content(CCC)and permeability of EICP-treated sands were measured.The validation of the model was confirmed through a comparative analysis of theoretical and experimental results.Furthermore,the impacts of porosity,particle size,CCC,and specific surface area on the hydraulic conductivity of EICP-treated sands were analyzed.The results showed that the model can reflect the hydraulic conductivity of EICP-treated sands under different particle size distributions and degrees of cementation,demonstrating broad applicability.Parametric analysis indicated the hydraulic conductivity gradually decreases with increasing CCC and specific surface area.Conversely,the hydraulic conductivity gradually increases with increasing porosity(n)and particle size(d50),with porosity exhibiting a significantly higher sensitivity than particle size.In summary,this study contributes theoretical foundations for the practical implementation of EICP technology in reducing soil permeability.展开更多
The dynamic evolution of fracture permeability presents a critical scientific challenge in rock masses.Understanding the mechanisms of rock mass permeability evolution is vital for engineering project design and opera...The dynamic evolution of fracture permeability presents a critical scientific challenge in rock masses.Understanding the mechanisms of rock mass permeability evolution is vital for engineering project design and operations.By integrating the discrete element method(DEM)with the finite element method(FEM),a numerical simulation framework for shear seepage in rough fractured shale has been developed to investigate the dynamic mechanisms of permeability evolution under varying confining pressures and during the shearing process.Numerical simulations were conducted on rough fractured samples under effective confining pressures ranging from 5 MPa to 20 MPa to monitor the aperture and permeability evolution of the fracture.The results of the numerical simulation are consistent with the experimental observations,indicating that both the shearing process and confining pressure significantly influence permeability.Moreover,the magnitude of the confining pressure is a crucial factor influencing the trend in permeability changes.Under a confining pressure of 5 MPa,fracture permeability initially increases significantly but decreases post-shearing.In contrast,a continuous decrease in fracture permeability is observed when the confining pressure exceeds 10 MPa.The results of the shear numerical simulation indicate that the confining pressure restricts fracture dilation during shearing,promotes the generation of rock debris,and decreases both the permeability and transmissivity of the fracture.The wear results obtained from numerical simulations are consistent with the experimental patterns and correlate with the joint roughness coefficient(JRC).This study proposed an effective numerical simulation method to reveal the evolution mechanism of fracture flow capacity,taking into account the wear of the fracture surface in shear simulations and the initial stress state of the rock in seepage simulations.This research explains the permeability evolution mechanism of fractured shale from a microscopic perspective,and the proposed numerical simulation method for shear seepage provides a powerful means to uncover the dynamic evolution mechanisms governing fracture permeability.展开更多
Hydraulic asphalt concrete(HAC)has been increasingly employed as an appropriate impervious structure in hydraulic and hydropower engineering.However,asphalt mortar,usually seen as the matrix of HAC composite,is partic...Hydraulic asphalt concrete(HAC)has been increasingly employed as an appropriate impervious structure in hydraulic and hydropower engineering.However,asphalt mortar,usually seen as the matrix of HAC composite,is particularly prone to damage under combined stress and seepage interactions,and the mesoscale investigations on the damage-seepage coupling behavior of HAC under complex stress states remain limited.This research develops a numerical three-dimensional mesoscale model composed of asphalt mortar and polyhedral aggregate to investigate the stress-damage-seepage coupling behavior in HAC.In this model,asphalt mortar yields the viscoelastic continuum damage law and aggregate obeys the Mazars’elastic-brittle damage law;simultaneously,the effective permeability coefficient of asphalt mortar is assumed to follow an exponential function of damage.The predicted deviatoric stress-strain and hydraulic gradient-seepage curves both are in good agreement with the reported experimental results,which shows the proposed model is valid and reasonable.The simulated results indicate that the damaged asphalt mortar can induce localized areas of high permeability,which in turn affects the overall impervious performance of HAC.展开更多
The physical properties of hydrocarbon reservoirs are important factors affecting the percolation ability of the reservoirs.Tight-sand reservoirs exhibit complex pore throat connectivity due to the extensive developme...The physical properties of hydrocarbon reservoirs are important factors affecting the percolation ability of the reservoirs.Tight-sand reservoirs exhibit complex pore throat connectivity due to the extensive development of micro-and nano-scale pore and throat systems.Characterizing the microscopic properties of these reservoirs using nondestructive,quantitative methods serves as an important means to determine the characteristics of microscopic pores and throats in tight-sand reservoirs and the mechanism behind the influence of these characteristics on reservoir porosity and permeability.In this study,a low-permeability sandstone sample and two tight sandstone samples collected from the Ordos Basin were nondestructively tested using high-resolution nano-CT technology to quantitively characterize their microscopic pore throat structures and model them three-dimensionally(in 3D)based on CT threshold differences and gray models.A thorough analysis and comparison reveal that the three samples exhibit a certain positive correlation between their porosity and permeability but the most important factor affecting both porosity and permeability is the microscopic pore throat structure.Although the number of pores in tight sandstones shows a minor impact on their porosity,large pores(more than 20μm)contribute predominantly to porosity,suggesting that the permeability of tight sandstones is controlled primarily by large pore throats.For these samples,higher permeability corresponds to larger average throat sizes.Therefore,throats with average radii greater than 2μm can significantly improve the permeability of tight sandstones.展开更多
Understanding the storage mechanisms in CO_(2)flooding is crucial,as many carbon capture,utilization,and storage(CCUS)projects are related to enhanced oil recovery(EOR).CO_(2)storage in reservoirs across large timesca...Understanding the storage mechanisms in CO_(2)flooding is crucial,as many carbon capture,utilization,and storage(CCUS)projects are related to enhanced oil recovery(EOR).CO_(2)storage in reservoirs across large timescales undergoes the two storage stages of oil displacement and well shut-in,which cover mul-tiple replacement processes of injection-production synchronization,injection only with no production,and injection-production stoppage.Because the controlling mechanism of CO_(2)storage in different stages is unknown,the evolution of CO_(2)storage mechanisms over large timescales is not understood.A math-ematical model for the evaluation of CO_(2)storage,including stratigraphic,residual,solubility,and mineral trapping in low-permeability tight sandstone reservoirs,was established using experimental and theoret-ical analyses.Based on a detailed geological model of the Huaziping Oilfield,calibrated with reservoir permeability and fracture characteristic parameters obtained from well test results,a dynamic simulation of CO_(2)storage for the entire reservoir life cycle under two scenarios of continuous injection and water-gas alternation were considered.The results show that CO_(2)storage exhibits the significant stage charac-teristics of complete storage,dynamic storage,and stable storage.The CO_(2)storage capacity and storage rate under the continuous gas injection scenario(scenario 1)were 6.34×10^(4)t and 61%,while those under the water-gas alternation scenario(scenario 2)were 4.62×10^(4)t and 46%.The proportions of stor-age capacity under scenarios 1 and 2 for structural or stratigraphic,residual,solubility,and mineral trap-ping were 33.36%,33.96%,32.43%,and 0.25%;and 15.09%,38.65%,45.77%,and 0.49%,respectively.The evolution of the CO_(2)storage mechanism showed an overall trend:stratigraphic and residual trapping first increased and then decreased,whereas solubility trapping gradually decreased,and mineral trapping continuously increased.Based on these results,an evolution diagram of the CO_(2)storage mechanism of low-permeability tight sandstone reservoirs across large timescales was established.展开更多
Irregular bone scaffolds fabricated using the Voronoi tessellation method resemble the morphology and properties of human cancellous bones.This has become a prominent topic in bone tissue engineering research in recen...Irregular bone scaffolds fabricated using the Voronoi tessellation method resemble the morphology and properties of human cancellous bones.This has become a prominent topic in bone tissue engineering research in recent years.However,studies on the radial-gradient design of irregular bionic scaffolds are limited.Therefore,this study aims to develop a radial-gradient structure similar to that of natural long bones,enhancing the development of bionic bone scaffolds.A novel gradient method was adopted to maintain constant porosity,control the seed site-specific distribution within the irregular porous structure,and vary the strut diameter to generate radial gradients.The irregular scaffolds were compared with four conventional scaffolds(cube,pillar BCC,vintiles,and diamond)in terms of permeability,stress concentration characteristics,and mechanical properties.The results indicate that the radial-gradient irregular porous structure boasts the widest permeability range and superior stress distribution compared to conventional scaffolds.With an elastic modulus ranging from 4.20 GPa to 22.96 GPa and a yield strength between 68.37 MPa and 149.40 MPa,it meets bone implant performance requirements and demonstrates significant application potential.展开更多
2'-Fucosyllactose(2'-FL)shows the potential to support intestinal health as a natural prebiotic that bridges the gap between infant formula feeding and breastfeeding.However,the effect and mechanism of 2'-...2'-Fucosyllactose(2'-FL)shows the potential to support intestinal health as a natural prebiotic that bridges the gap between infant formula feeding and breastfeeding.However,the effect and mechanism of 2'-FL in improving intestinal permeability are not clear.In this study,we constructed human microbiota-associated(HMA)mouse models by colonizing healthy infant feces in mice with antibiotic-depleted intestinal microbiota.The protective effect of 2'-FL on the intestinal permeability was explored using the HMA mouse models,and the combination of metagenomics was used to analyze the possible mechanisms by which the microorganisms reduced the intestinal permeability.The results showed that 2'-FL decreased the concentration of markers of intestinal permeability(enterotoxin and diamine oxidase(DAO))and increased the expression levels of tight junctions(occludin and claudin).Metagenomics revealed the enrichment of Bifidobacterium and increased the expression of glycoside hydrolases(GHs),including GH31,GH28,and GH5.In conclusion,2'-FL strengthened intestinal permeability function by improving microbiota composition to control the translocation of harmful substance.展开更多
CO_(2)flooding enhanced oil recovery(CO_(2)-EOR)represents a significant technology in the low permeability reservoir.With the fractures and heterogeneity in low permeability reservoirs,CO_(2)-EOR is susceptible to pe...CO_(2)flooding enhanced oil recovery(CO_(2)-EOR)represents a significant technology in the low permeability reservoir.With the fractures and heterogeneity in low permeability reservoirs,CO_(2)-EOR is susceptible to pessimistic gas channeling.Consequently,there is a need to develop conformance control materials that can be used in CO_(2)-EOR.Herein,to address the challenges of low strength and poor stability of polymer gel in high temperature and low permeability reservoirs,a new organic/metal ion composite crosslinking polymer gel(AR-Gel)is reported,which is formed by low hydrolysis and medium to high molecular weight polymer(CX-305),organic crosslinking agent(phenolic resin),and aluminium citrate(AI(Ⅲ)).The crosslinking of AI(Ⅲ)with carboxyl group and organic/metal ion double crosslinking can construct a more complex and stable polymer gel structure on the basis of traditional chemical crosslinking,to cope with the harsh conditions such as high temperature.The structure-activity relationship of AR-Gel was revealed by rheology behavior and micro-morphology.The applicability of AR-Gel in reservoir was investigated,as was its strength and stability in supercritical CO_(2).The anti-gas channeling and enhanced oil recovery of AR-Gel were investigated using low permeability fractured cores,and the field process parameters were provided.The gel can be used to meet supercritical CO_(2)reservoirs at 110℃and 20,000 mg/L salinity,with long-term stability over 60 days.The plugging rate of AR-Gel for fractured co re was 97%,with subsequent CO_(2)flooding re sulting in an enhanced oil recovery by 34.5%.ARGel can effectively control CO_(2)gas channeling and enhanced oil recovery.It offers a new material with high strength and temperature resistance,which is particularly beneficial in the CO_(2)flooding for the conformance control of oil field.展开更多
Triggered seismicity is a key hazard where fluids are injected or withdrawn from the subsurface and may impact permeability. Understanding the mechanisms that control fluid injection-triggered seismicity allows its mi...Triggered seismicity is a key hazard where fluids are injected or withdrawn from the subsurface and may impact permeability. Understanding the mechanisms that control fluid injection-triggered seismicity allows its mitigation. Key controls on seismicity are defined in terms of fault and fracture strength, second-order frictional response and stability, and competing fluid-driven mechanisms for arrest. We desire to constrain maximum event magnitudes in triggered earthquakes by relating pre-existing critical stresses to fluid injection volume to explain why some recorded events are significantly larger than anticipated seismic moment thresholds. This formalism is consistent with several uncharacteristically large fluid injection-triggered earthquakes. Such methods of reactivating fractures and faults by hydraulic stimulation in shear or tensile fracturing are routinely used to create permeability in the subsurface. Microearthquakes (MEQs) generated by such stimulations can be used to diagnose permeability evolution. Although high-fidelity data sets are scarce, the EGS-Collab and Utah FORGE hydraulic stimulation field demonstration projects provide high-fidelity data sets that concurrently track permeability evolution and triggered seismicity. Machine learning deciphers the principal features of MEQs and the resulting permeability evolution that best track permeability changes – with transfer learning methods allowing robust predictions across multiple eological settings. Changes in permeability at reactivated fractures in both shear and extensional modes suggest that permeability change (Δk) scales with the seismic moment (M) of individual MEQs as Δk∝M. This scaling relation is exact at early times but degrades with successive MEQs, but provides a method for characterizing crustal permeability evolution using MEQs, alone. Importantly, we quantify for the first time the role of prestress in defining the elevated magnitude and seismic moment of fluid injection-triggered events, and demonstrate that such MEQs can also be used as diagnostic in quantifying permeability evolution in the crust.展开更多
The strength of the sliding zone soil determines the stability of reservoir landslides.Fluctuations in water levels cause a change in the seepage field,which serves as both the external hydrogeological environment and...The strength of the sliding zone soil determines the stability of reservoir landslides.Fluctuations in water levels cause a change in the seepage field,which serves as both the external hydrogeological environment and the internal component of a landslide.Therefore,considering the strength changes of the sliding zone with seepage effects,they correspond with the actual hydrogeological circumstances.To investigate the shear behavior of sliding zone soil under various seepage pressures,24 samples were conducted by a self-developed apparatus to observe the shear strength and measure the permeability coefficients at different deformation stages.After seepage-shear tests,the composition of clay minerals and microscopic structure on the shear surface were analyzed through X-ray and scanning electron microscope(SEM)to understand the coupling effects of seepage on strength.The results revealed that the sliding zone soil exhibited strain-hardening without seepage pressure.However,the introduction of seepage caused a significant reduction in shear strength,resulting in strain-softening characterized by a three-stage process.Long-term seepage action softened clay particles and transported broken particles into effective seepage channels,causing continuous damage to the interior structure and reducing the permeability coefficient.Increased seepage pressure decreased the peak strength by disrupting occlusal and frictional forces between sliding zone soil particles,which carried away more clay particles,contributing to an overhead structure in the soil that raised the permeability coefficient and decreased residual strength.The internal friction angle was less sensitive to variations in seepage pressure than cohesion.展开更多
As the first gold mine discovered at the sea in China and the only coastal gold mine currently mined there,Sanshandao Gold Mine faces unique challenges.The mine's safety is under continual threat from its faulted ...As the first gold mine discovered at the sea in China and the only coastal gold mine currently mined there,Sanshandao Gold Mine faces unique challenges.The mine's safety is under continual threat from its faulted structure coupled with the overlying water.As the mining proceeds deeper,the risk of water inrush increases.The mine's maximum water yield reaches 15000 m3/day,which is attributable to water channels present in fault zones.Predominantly composed of soil–rock mixtures(SRM),these fault zones'seepage characteristics significantly impact water inrush risk.Consequently,investigating the seepage characteristics of SRM is of paramount importance.However,the existing literature mostly concentrates on a single stress state.Therefore,this study examined the characteristics of the permeability coefficient under three distinct stress states:osmotic,osmotic–uniaxial,and osmotic–triaxial pressure.The SRM samples utilized in this study were extracted from in situ fault zones and then reshaped in the laboratory.In addition,the micromechanical properties of the SRM samples were analyzed using computed tomography scanning.The findings reveal that the permeability coefficient is the highest under osmotic pressure and lowest under osmotic–triaxial pressure.The sensitivity coefficient shows a higher value when the rock block percentage ranges between 30%and 40%,but it falls below 1.0 when this percentage exceeds 50%under no confining pressure.Notably,rock block percentages of 40%and 60%represent the two peak points of the sensitivity coefficient under osmotic–triaxial pressure.However,SRM samples with a 40%rock block percentage consistently show the lowest permeability coefficient under all stress states.This study establishes that a power function can model the relationship between the permeability coefficient and osmotic pressure,while its relationship with axial pressure can be described using an exponential function.These insights are invaluable for developing water inrush prevention and control strategies in mining environments.展开更多
It has been well recognized that sand particles significantly affect the mechanical properties of reconstituted sandy clays,including the hosted clay and sand particles.However,interrelation between the permeability a...It has been well recognized that sand particles significantly affect the mechanical properties of reconstituted sandy clays,including the hosted clay and sand particles.However,interrelation between the permeability and compressibility of reconstituted sandy clays by considering the structural effects of sand particles is still rarely reported.For this,a series of consolidation-permeability coefficient tests were conducted on reconstituted sandy clays with different sand fractions(ψ_(ss)),initial void ratio of hosted clays(e_(c0))and void ratio at liquid limit of hosted clays(e_(cL)).The roles of ψ_(ss) in both the relationships of permeability coefficient of hosted clay(k_(v-hosted clay))versus effective vertical stress(σ'_(v))and void ratio of hosted clay(e_(c-hosted clay))versus σ'_(v) were analyzed.The results show that the permeability coefficient of reconstituted sandy clays(k_(v))is dominated by hosted clay(k_(v)=k_(v-hosted clay)).Both ψ_(ss) and σ'_(v) affect the k_(v) of sandy clays by changing the e_(c-hosted clay) at any given σ'_(v).Due to the partial contacts and densified clay bridges between the sand particles(i.e.structure effects),the e_(c-hosted clay) in sandy clays is higher than that in clays at the same σ'_(v)v.The k_(v)-e_(c-hosted clay) relationship of sandy clays is independent of σ'_(v) and ψ_(ss)but is a function of e_(cL).The types of hosted clays affect the k_(v) of sandy clays by changing the e_(cL).Based on the relationship between permeability coefficient and void ratio for the reconstituted clays,an empirical method for determining the k_(v) is proposed and validated for sandy clays.The predicted values are almost consistent with the measured values with k_(v-predicted)=k_(v-measured)=0.6-2.5.展开更多
Clayey-silt natural gas hydrate reservoirs in the South China Sea exhibit loose and unconsolidated structures, heterogeneous pore structures, high clay mineral contents, and strong hydrophilicity. These characteristic...Clayey-silt natural gas hydrate reservoirs in the South China Sea exhibit loose and unconsolidated structures, heterogeneous pore structures, high clay mineral contents, and strong hydrophilicity. These characteristics complicate the gas-water two-phase flow process in porous media following hydrate decomposition, posing challenges for efficient development. This study examines the transport response of clayey-silt reservoir samples from the Shenhu area using gas-water two-phase flow experiments and CT scanning to explore changes in pore structure, gas-water distribution, and relative permeability under varying flow conditions. The results indicate that pore heterogeneity significantly influences flow characteristics. Gas preferentially displaces water in larger pores, forming fracture-like pores, which serve as preferential flow channels for gas migration. The preferential flow channels enhance gas-phase permeability up to 19 times that of the water phase when fluid pressures exceed total stresses. However,small pores retain liquid, leading to a high residual water saturation of 0.561. CT imaging reveals that these hydro-fractures improve gas permeability but also confine gas flow to specific channels. Pore network analysis shows that gas injection expands the pore-throat network, enhancing connectivity and forming fracture-like pores. Residual water remains trapped in smaller pores and throats, while structural changes, including new fractures, improve gas flow pathways and overall connectivity. Relative permeability curves demonstrate a narrow gas-water cocurrent-flow zone, a right-shifted iso-permeability point and high reservoir capillary pressure, indicating a strong "water-blocking" effect. The findings suggest that optimizing reservoir stimulation techniques to enhance fracture formation, reduce residual water saturation, and improve gas flow capacity is critical for efficient hydrate reservoir development.展开更多
Understanding the relationship between normal stiffness and permeability in rock fractures under high and true-triaxial in situ stress conditions is critical to assess hydro-mechanical coupling in the Earth's crus...Understanding the relationship between normal stiffness and permeability in rock fractures under high and true-triaxial in situ stress conditions is critical to assess hydro-mechanical coupling in the Earth's crust.Previous data on stiffness–permeability relations are measured under uniaxial stress states as well as under normal stress.However,many projects involve faulted formations with complex three-dimensional(3D)stress states or significant changes to the original stress state.We rectified this by following the permeability evolution using a true-triaxial stress-permeability apparatus as well as independently applying a spectrum of triaxial stresses from low to high.The relationship between permeability and fracture normal stiffness was quantified using constraints based on the principle of virtual work.The impacts of fracture-lateral and fracture-normal stresses on permeability and normal stiffness evolution were measured.It was found that permeability decreases with increasing fracture-lateral and fracture-normal stresses as a result of Poisson confinement,independent of the orientation of the fracture relative to the stresses.The lateral stresses dominated the evolution of normal stiffness at lower normal stresses(σ_(3)=10 MPa)and played a supplementary role at higher normal stresses(σ_(3)>10 MPa).Moreover,correlations between the evolution of permeability and normal stiffness were extended beyond the low-stiffness,high-permeability region to the high-stiffness,low-permeability region under high fracture-lateral stresses(10–80 MPa)with fracture-normal stress(10–50 MPa)conditions.Again,high lateral stresses further confined the fracture and therefore reduced permeability and increased normal stiffness,which exceeded the previous reported stiffness under no lateral stress conditions.This process enabled us to identify a fundamental change in the flow regime from multi-channel to isolated channelized flow.These results provide important characterizations of fracture permeability in the deep crust,including recovery from deep shale-gas reservoirs.展开更多
The structural integrity of the interface between a concrete plug and the surrounding rock may be compromised during frequent cycles of air charging,discharging,and storage,which is typical of compressed air energy st...The structural integrity of the interface between a concrete plug and the surrounding rock may be compromised during frequent cycles of air charging,discharging,and storage,which is typical of compressed air energy storage systems in abandoned mines.To investigate this,nitrogen permeability tests were conducted on the interface samples of rockeconcrete interface in both consolidated and unconsolidated states under cyclic loading.The variations in the flow rate throughout the permeability process under different cycle numbers and load range conditions were investigated.The microscopic analysis at the interfaces was imaged using computed tomography scanning.The results indicated that the gas permeability of the cemented interfaces with different roughness values varied with confining pressure ranging from 10^(-13) m^(2) to 10^(-12) m^(2),whereas that of the non-cemented interfaces ranged from 10^(-12) m^(2) to 10^(-11) m^(2).A larger load variation range encompassed the permeability variation characteristics within a smaller variation range.The evolution pattern of the permeability ratio with the number of cycles was influenced by the inlet pressure.The greater the inlet pressure,the larger the increment ratio of the permeability.The permeability change patterns of interfaces with different roughness values were similar.Microscopic analysis revealed that pores inside the concrete were connected to the interface gaps.Under the coupling of stress and gas pressure,the gas could penetrate the crack tips or pores,accelerating the development of microcracks during the cyclic opening and closing of the pores.This study provides valuable insights into the safe long-term operation of underground high-pressure air storage.展开更多
Phenolic resin-based porous composites are the promising thermal protection materials for aerospace applications.The high-temperature evolution of microstructure due to the decomposition of the resin also presents gre...Phenolic resin-based porous composites are the promising thermal protection materials for aerospace applications.The high-temperature evolution of microstructure due to the decomposition of the resin also presents great challenges to predict the internal heat and mass transport behaviors.This work investigates the effects of microstructural characteristics such as the number of pores,size distribution,pore-throats size and volume fraction on the permeation behaviors of fluid in the needle-punched short-cut fiber reinforced silicon phenolic resin-based porous composites.The specimens are prepared by the sol-gel method and the atmospheric pressure drying process and the pyrolysis experiment are conducted at 400℃and 800℃.Then,a scanning electron microscope and a Nano-CT computer tomography are applied to obtain the surface morphologies and the interior slice images of the specimens.The AVIZO software is employed to accurately extract and analyze the pore structural model and simulated calculate the absolute permeability.It is found that the small pores develop gradually during pyrolysis due to the resin decomposition and the quartz fibers rearrangement,resulting in an increase in number of large pores.Nonetheless,the equivalent radii of most pores are less than 1μm.Very few pores possess a large radius over 5μm.However,the volume fraction of these large pores exceeds 99%.In addition,with the pore size growing,the connectivity between these pores is enhanced,immediately causing an increase in number and size of the pore-throats.Larger pore and more pore-throats would add the unblocked flow channels for the fluid passing,reducing flow resistance.The seepage simulation also confirms that the absolute permeability gains significant increase after pyrolysis in all directions.For example,the absolute permeability of the pyrolyzed sample is 9.0×10^(-13)m^(2) in X direction,which is an order of magnitude greater than that of the unpyrolyzed sample.This study provides important insights for understanding the high-temperature evolution at of microstructure and the permeation behavior of fluid in porous thermal protection materials.展开更多
In subsurface projects where the host rock is of low permeability,fractures play an important role in fluid circulation.Both the geometrical and mechanical properties of the fracture are relevant to the permeability o...In subsurface projects where the host rock is of low permeability,fractures play an important role in fluid circulation.Both the geometrical and mechanical properties of the fracture are relevant to the permeability of the fracture.To evaluate this relationship,we numerically generated self-affine fractures reproducing the scaling relationship of the power spectral density(PSD)of the measured fracture surfaces.The fractures were then subjected to a uniform and stepwise increase in normal stress.A fast Fourier transform(FFT)-based elastic contact model was used to simulate the fracture closure.The evolution of fracture contact area,fracture closure,and fracture normal stiffness were determined throughout the whole process.In addition,the fracture permeability at each step was calculated by the local cubic law(LCL).The influences of roughness exponent and correlation length on the fracture hydraulic and mechanical behaviors were investigated.Based on the power law of normal stiffness versus normal stress,the corrected cubic law and the linear relationship between fracture closure and mechanical aperture were obtained from numerical modeling of a set of fractures.Then,we derived a fracture normal stiffness-permeability equation which incorporates fracture geometric parameters such as the root-mean-square(RMS),roughness exponent,and correlation length,which can describe the fracture flow under an effective medium regime and a percolation regime.Finally,we interpreted the flow transition behavior from the effective medium regime to the percolation regime during fracture closure with the established stiffness-permeability function.展开更多
In view of the increased focus on“green”and sustainable development and compliance with the national strategy for“carbon peak and carbon neutrality,”this study investigated the effect of replacing cement(0-20%)wit...In view of the increased focus on“green”and sustainable development and compliance with the national strategy for“carbon peak and carbon neutrality,”this study investigated the effect of replacing cement(0-20%)with limestone powder(stone powder)as a mineral admixture on the micro,meso,and macro properties of mortar.First,the applicability of stone powder was examined based on the physical filling and heat of hydration of stone powder-cement.Second,micro-meso testing methods,such as X-ray diffraction,scanning electron microscopy,thermogravimetry-differential scanning calorimetry,and nuclear magnetic resonance,were utilized to reveal the influencing mechanisms of stone powder on the microstructure of the mortar.Furthermore,the effect of stone powder on the compressive strength and gas permeability of the mortar was analyzed.Additionally,the time-dependent variations in the gas permeability and its functional relationship with the mechanical properties were determined.Finally,the correlation between the compressive strength and gas permeability with respect to the pore size of stone powder-doped mortar was established via gray-correlation analysis.The results show that an appropriate amount of stone powder(5%)can effectively improve the particle gradation,decelerate the release of the heat of hydration,increase the amount of hydration products,and improve the pore structure,thereby increasing the compressive strength and reducing the gas permeability coefficient.The gas permeability of stone powder-doped mortar was found to exhibit good time-dependent characteristics as well as a quadratic linear correlation with the compressive strength.The gray-correlation analysis results indicate that air pores exhibit the highest influence on the compressive strength and that the gas permeability coefficient is most significantly affected by large pores.展开更多
基金supported by the National Natural Science Foundation of China(Nos.U22A20165 and 52474156)the Key Research and Development Program of Xinjiang Uyghur Autonomous Region(No.2023B01010-1)the China Scholarship Council(No.202406420054).
文摘Water inrush hazards from the floor strata of longwall workingface are commonly encountered in North China coalfields,which essentially result from the evolution of permeability in the floor rock under complex mining-induced stress conditions.Current research rarely addresses the evolution of rock permeability under such complex stress paths.Describing this evolution using only one stress parameter,such as effective stress,deviatoric stress,axial stress,or confining stress,is highly challenging.In this study,we developed a laboratory loading scheme that simulates mining-induced stress evolution.Hydro-mechanical experiments were conducted to investigate the evolution of rock permeability under mining stress.The mechanism on the change of stress-permeability relationships in mining-disturbed rock is revealed,supporting to the analysis of management strategies for floor water-inrush disasters.The results show that rock permeability evolves through four stages,including rapid decline,gradual fluctuation,sharp increase,and slow attenuation.1–2 permeability surges occurred during mining-stress loading,closely linked to the emergence and reversal of deviatoric stress in magnitude and direction.With the first permeability surge,the deviatoric stress within the mudstone reached approximately 1.7 MPa,whereas that of the sandstone was about 1 MPa.The second permeability surge in the mudstone corresponded to the secondary rotation of the principal stress direction.CT and ultrasonic tests suggested an increase in microcracks in both rocks during the first permeability surge.However,the deviatoric stress-permeability plot before and after mining indicated that the fracture of mudstone sample changed significantly,while that of the sandstone remained unchanged.The permeability surges observed at different stages are interpreted as resulting from shear-induced reopening of pre-existing fractures and the formation of new shear-failure fractures.A stress-permeability model jointly governed by effective mean stress and deviatoric stress was established.Furthermore,two strategies are proposed for the floor water-inrush disasters prevention,(i)timely backfilling to reduce deviatoric stress,(ii)grouting after the first permeability surge.This work provides insights into stress-seepage behavior in rocks under complex stress evolution and offers new perspectives for identifying potential water inrush pathways in the floor strata of coal seam during longwall mining.
基金National Natural Science Foundation of China,Grant/Award Numbers:52274082,42307244,42230704Jiangxi Provincial Natural Science Foundation,Grant/Award Number:2024BAB26047+3 种基金Innovative Experts,Long-term Program of Jiangxi Province,Grant/Award Number:jxsq2018106049Opening Foundation of Anhui Province Key Laboratory of Building Structure and Underground Engineering,Grant/Award Number:KLBSUE‐2022‐04Program of Qingjiang Excellent Young Talents of Jiangxi University of Science and Technology,Grant/Award Number:JXUSTQJBJ2020003Fundamental Research Funds for the Central Universities,Grant/Award Number:2023QN1024。
文摘Prediction of permeability changes in surrounding rock induced by engineering disturbances is crucial for mitigating tunnel water inrush accidents.This study investigates the progressive failure characteristics and permeability evolution of hard and soft rocks subjected to triaxial compression.A series of laboratory tests were conducted at confining pressures ranging from 4 to 20 MPa.Experimental results demonstrate that rock permeability variation with strain shows three distinct stages:an initial decrease,a stage of rapid mutation,and a postpeak increase.The concept of critical permeability barrier strength is introduced,representing the stress level at which continuous fracture formation enables significant seepage.Furthermore,two generalized permeability–stress models are developed for soft and hard rocks.The predicted permeability values obtained from these models align well with the experimental data.These findings offer valuable insights into the hydro-mechanical coupling behavior of rocks,providing a foundation for safe construction practices in underground engineering.
基金supported by the National Youth Top-notch Talent Support Program of China(Grant No.00389335)the National Natural Science Foundation of China(Grant No.52378392)the“Foal Eagle Program”Youth Top-notch Talent Project of Fujian Province,China(Grant No.00387088).
文摘Enzyme-induced carbonate precipitation(EICP)is a potential ground improvement method that can reduce the permeability of sands.However,the traditional mathematical models are hard to accurately predict the permeability of EICP-treated sands.In this study,the mathematical model was established for predicting the permeability of EICP-treated sands based on Kozeny-Carman equation.The effects of calcium carbonate precipitation on the porosity,tortuosity,and specific surface area of the EICP-treated sands were considered in the model.To validate the model,the bio-cemented sand column tests with different grain size distributions(coarse,medium,and fine sands)and treatment numbers(6,8,and 10 times)were conducted.The calcium carbonate content(CCC)and permeability of EICP-treated sands were measured.The validation of the model was confirmed through a comparative analysis of theoretical and experimental results.Furthermore,the impacts of porosity,particle size,CCC,and specific surface area on the hydraulic conductivity of EICP-treated sands were analyzed.The results showed that the model can reflect the hydraulic conductivity of EICP-treated sands under different particle size distributions and degrees of cementation,demonstrating broad applicability.Parametric analysis indicated the hydraulic conductivity gradually decreases with increasing CCC and specific surface area.Conversely,the hydraulic conductivity gradually increases with increasing porosity(n)and particle size(d50),with porosity exhibiting a significantly higher sensitivity than particle size.In summary,this study contributes theoretical foundations for the practical implementation of EICP technology in reducing soil permeability.
基金funded by the Joint Funds of the National Natural Science Foundation of China(Grant No.U23A20671)the Major Project of Inner Mongolia Science and Technology(Grant No.2021ZD0034)the Open Research Fund of State Key Laboratory of Geomechanics and Geotechnical Engi-neering(Grant No.Z021003).
文摘The dynamic evolution of fracture permeability presents a critical scientific challenge in rock masses.Understanding the mechanisms of rock mass permeability evolution is vital for engineering project design and operations.By integrating the discrete element method(DEM)with the finite element method(FEM),a numerical simulation framework for shear seepage in rough fractured shale has been developed to investigate the dynamic mechanisms of permeability evolution under varying confining pressures and during the shearing process.Numerical simulations were conducted on rough fractured samples under effective confining pressures ranging from 5 MPa to 20 MPa to monitor the aperture and permeability evolution of the fracture.The results of the numerical simulation are consistent with the experimental observations,indicating that both the shearing process and confining pressure significantly influence permeability.Moreover,the magnitude of the confining pressure is a crucial factor influencing the trend in permeability changes.Under a confining pressure of 5 MPa,fracture permeability initially increases significantly but decreases post-shearing.In contrast,a continuous decrease in fracture permeability is observed when the confining pressure exceeds 10 MPa.The results of the shear numerical simulation indicate that the confining pressure restricts fracture dilation during shearing,promotes the generation of rock debris,and decreases both the permeability and transmissivity of the fracture.The wear results obtained from numerical simulations are consistent with the experimental patterns and correlate with the joint roughness coefficient(JRC).This study proposed an effective numerical simulation method to reveal the evolution mechanism of fracture flow capacity,taking into account the wear of the fracture surface in shear simulations and the initial stress state of the rock in seepage simulations.This research explains the permeability evolution mechanism of fractured shale from a microscopic perspective,and the proposed numerical simulation method for shear seepage provides a powerful means to uncover the dynamic evolution mechanisms governing fracture permeability.
基金supported by the National Key Research and Development Program of China(Grant No.2022YFC3005603-01)the Natural Science Foundation Science of Anhui Province(Grant No.2308085US02).
文摘Hydraulic asphalt concrete(HAC)has been increasingly employed as an appropriate impervious structure in hydraulic and hydropower engineering.However,asphalt mortar,usually seen as the matrix of HAC composite,is particularly prone to damage under combined stress and seepage interactions,and the mesoscale investigations on the damage-seepage coupling behavior of HAC under complex stress states remain limited.This research develops a numerical three-dimensional mesoscale model composed of asphalt mortar and polyhedral aggregate to investigate the stress-damage-seepage coupling behavior in HAC.In this model,asphalt mortar yields the viscoelastic continuum damage law and aggregate obeys the Mazars’elastic-brittle damage law;simultaneously,the effective permeability coefficient of asphalt mortar is assumed to follow an exponential function of damage.The predicted deviatoric stress-strain and hydraulic gradient-seepage curves both are in good agreement with the reported experimental results,which shows the proposed model is valid and reasonable.The simulated results indicate that the damaged asphalt mortar can induce localized areas of high permeability,which in turn affects the overall impervious performance of HAC.
文摘The physical properties of hydrocarbon reservoirs are important factors affecting the percolation ability of the reservoirs.Tight-sand reservoirs exhibit complex pore throat connectivity due to the extensive development of micro-and nano-scale pore and throat systems.Characterizing the microscopic properties of these reservoirs using nondestructive,quantitative methods serves as an important means to determine the characteristics of microscopic pores and throats in tight-sand reservoirs and the mechanism behind the influence of these characteristics on reservoir porosity and permeability.In this study,a low-permeability sandstone sample and two tight sandstone samples collected from the Ordos Basin were nondestructively tested using high-resolution nano-CT technology to quantitively characterize their microscopic pore throat structures and model them three-dimensionally(in 3D)based on CT threshold differences and gray models.A thorough analysis and comparison reveal that the three samples exhibit a certain positive correlation between their porosity and permeability but the most important factor affecting both porosity and permeability is the microscopic pore throat structure.Although the number of pores in tight sandstones shows a minor impact on their porosity,large pores(more than 20μm)contribute predominantly to porosity,suggesting that the permeability of tight sandstones is controlled primarily by large pore throats.For these samples,higher permeability corresponds to larger average throat sizes.Therefore,throats with average radii greater than 2μm can significantly improve the permeability of tight sandstones.
基金supported by the National Key Research and Development Program of China(2022YFE0206700).
文摘Understanding the storage mechanisms in CO_(2)flooding is crucial,as many carbon capture,utilization,and storage(CCUS)projects are related to enhanced oil recovery(EOR).CO_(2)storage in reservoirs across large timescales undergoes the two storage stages of oil displacement and well shut-in,which cover mul-tiple replacement processes of injection-production synchronization,injection only with no production,and injection-production stoppage.Because the controlling mechanism of CO_(2)storage in different stages is unknown,the evolution of CO_(2)storage mechanisms over large timescales is not understood.A math-ematical model for the evaluation of CO_(2)storage,including stratigraphic,residual,solubility,and mineral trapping in low-permeability tight sandstone reservoirs,was established using experimental and theoret-ical analyses.Based on a detailed geological model of the Huaziping Oilfield,calibrated with reservoir permeability and fracture characteristic parameters obtained from well test results,a dynamic simulation of CO_(2)storage for the entire reservoir life cycle under two scenarios of continuous injection and water-gas alternation were considered.The results show that CO_(2)storage exhibits the significant stage charac-teristics of complete storage,dynamic storage,and stable storage.The CO_(2)storage capacity and storage rate under the continuous gas injection scenario(scenario 1)were 6.34×10^(4)t and 61%,while those under the water-gas alternation scenario(scenario 2)were 4.62×10^(4)t and 46%.The proportions of stor-age capacity under scenarios 1 and 2 for structural or stratigraphic,residual,solubility,and mineral trap-ping were 33.36%,33.96%,32.43%,and 0.25%;and 15.09%,38.65%,45.77%,and 0.49%,respectively.The evolution of the CO_(2)storage mechanism showed an overall trend:stratigraphic and residual trapping first increased and then decreased,whereas solubility trapping gradually decreased,and mineral trapping continuously increased.Based on these results,an evolution diagram of the CO_(2)storage mechanism of low-permeability tight sandstone reservoirs across large timescales was established.
基金the National Natural Science Foundation of China(No.52165026)。
文摘Irregular bone scaffolds fabricated using the Voronoi tessellation method resemble the morphology and properties of human cancellous bones.This has become a prominent topic in bone tissue engineering research in recent years.However,studies on the radial-gradient design of irregular bionic scaffolds are limited.Therefore,this study aims to develop a radial-gradient structure similar to that of natural long bones,enhancing the development of bionic bone scaffolds.A novel gradient method was adopted to maintain constant porosity,control the seed site-specific distribution within the irregular porous structure,and vary the strut diameter to generate radial gradients.The irregular scaffolds were compared with four conventional scaffolds(cube,pillar BCC,vintiles,and diamond)in terms of permeability,stress concentration characteristics,and mechanical properties.The results indicate that the radial-gradient irregular porous structure boasts the widest permeability range and superior stress distribution compared to conventional scaffolds.With an elastic modulus ranging from 4.20 GPa to 22.96 GPa and a yield strength between 68.37 MPa and 149.40 MPa,it meets bone implant performance requirements and demonstrates significant application potential.
基金financially supported by the National Key Research and Development Program of China(2022YFF1100402)National Center of Technology Innovation for Dairy(2022-Open subject-11)+1 种基金Young Elite Scientist Sponsorship Program by CAST(YESS20200271)the National Natural Science Foundation of China(32101919)。
文摘2'-Fucosyllactose(2'-FL)shows the potential to support intestinal health as a natural prebiotic that bridges the gap between infant formula feeding and breastfeeding.However,the effect and mechanism of 2'-FL in improving intestinal permeability are not clear.In this study,we constructed human microbiota-associated(HMA)mouse models by colonizing healthy infant feces in mice with antibiotic-depleted intestinal microbiota.The protective effect of 2'-FL on the intestinal permeability was explored using the HMA mouse models,and the combination of metagenomics was used to analyze the possible mechanisms by which the microorganisms reduced the intestinal permeability.The results showed that 2'-FL decreased the concentration of markers of intestinal permeability(enterotoxin and diamine oxidase(DAO))and increased the expression levels of tight junctions(occludin and claudin).Metagenomics revealed the enrichment of Bifidobacterium and increased the expression of glycoside hydrolases(GHs),including GH31,GH28,and GH5.In conclusion,2'-FL strengthened intestinal permeability function by improving microbiota composition to control the translocation of harmful substance.
基金project was supported by the Fund of State Key Laboratory of Deep Oil and Gas,China University of Petroleum(East China)(No.SKLDOG2024-ZYRC-06)Key Program of National Natural Science Foundation of China(52130401)+1 种基金National Natural Science Foundation of China(52104055,52374058)Shandong Provincial Natural Science Foundation,China(ZR2021ME171,ZR2024YQ043)。
文摘CO_(2)flooding enhanced oil recovery(CO_(2)-EOR)represents a significant technology in the low permeability reservoir.With the fractures and heterogeneity in low permeability reservoirs,CO_(2)-EOR is susceptible to pessimistic gas channeling.Consequently,there is a need to develop conformance control materials that can be used in CO_(2)-EOR.Herein,to address the challenges of low strength and poor stability of polymer gel in high temperature and low permeability reservoirs,a new organic/metal ion composite crosslinking polymer gel(AR-Gel)is reported,which is formed by low hydrolysis and medium to high molecular weight polymer(CX-305),organic crosslinking agent(phenolic resin),and aluminium citrate(AI(Ⅲ)).The crosslinking of AI(Ⅲ)with carboxyl group and organic/metal ion double crosslinking can construct a more complex and stable polymer gel structure on the basis of traditional chemical crosslinking,to cope with the harsh conditions such as high temperature.The structure-activity relationship of AR-Gel was revealed by rheology behavior and micro-morphology.The applicability of AR-Gel in reservoir was investigated,as was its strength and stability in supercritical CO_(2).The anti-gas channeling and enhanced oil recovery of AR-Gel were investigated using low permeability fractured cores,and the field process parameters were provided.The gel can be used to meet supercritical CO_(2)reservoirs at 110℃and 20,000 mg/L salinity,with long-term stability over 60 days.The plugging rate of AR-Gel for fractured co re was 97%,with subsequent CO_(2)flooding re sulting in an enhanced oil recovery by 34.5%.ARGel can effectively control CO_(2)gas channeling and enhanced oil recovery.It offers a new material with high strength and temperature resistance,which is particularly beneficial in the CO_(2)flooding for the conformance control of oil field.
基金Derek Elsworth acknowledges the support from a Gledden Visiting Fellowship from the Institute of Advanced Studies at the University of Western Australia,Australia,and the G.Albert Shoemaker Endowment at Pennsylvania State University,USA.
文摘Triggered seismicity is a key hazard where fluids are injected or withdrawn from the subsurface and may impact permeability. Understanding the mechanisms that control fluid injection-triggered seismicity allows its mitigation. Key controls on seismicity are defined in terms of fault and fracture strength, second-order frictional response and stability, and competing fluid-driven mechanisms for arrest. We desire to constrain maximum event magnitudes in triggered earthquakes by relating pre-existing critical stresses to fluid injection volume to explain why some recorded events are significantly larger than anticipated seismic moment thresholds. This formalism is consistent with several uncharacteristically large fluid injection-triggered earthquakes. Such methods of reactivating fractures and faults by hydraulic stimulation in shear or tensile fracturing are routinely used to create permeability in the subsurface. Microearthquakes (MEQs) generated by such stimulations can be used to diagnose permeability evolution. Although high-fidelity data sets are scarce, the EGS-Collab and Utah FORGE hydraulic stimulation field demonstration projects provide high-fidelity data sets that concurrently track permeability evolution and triggered seismicity. Machine learning deciphers the principal features of MEQs and the resulting permeability evolution that best track permeability changes – with transfer learning methods allowing robust predictions across multiple eological settings. Changes in permeability at reactivated fractures in both shear and extensional modes suggest that permeability change (Δk) scales with the seismic moment (M) of individual MEQs as Δk∝M. This scaling relation is exact at early times but degrades with successive MEQs, but provides a method for characterizing crustal permeability evolution using MEQs, alone. Importantly, we quantify for the first time the role of prestress in defining the elevated magnitude and seismic moment of fluid injection-triggered events, and demonstrate that such MEQs can also be used as diagnostic in quantifying permeability evolution in the crust.
基金supported by the Major Program of the National Natural Science Foundation of China (Grant No.42090055)the National Major Scientific Instruments and Equipment Development Projects of China (Grant No.41827808)the National Nature Science Foundation of China (Grant No.42207216).
文摘The strength of the sliding zone soil determines the stability of reservoir landslides.Fluctuations in water levels cause a change in the seepage field,which serves as both the external hydrogeological environment and the internal component of a landslide.Therefore,considering the strength changes of the sliding zone with seepage effects,they correspond with the actual hydrogeological circumstances.To investigate the shear behavior of sliding zone soil under various seepage pressures,24 samples were conducted by a self-developed apparatus to observe the shear strength and measure the permeability coefficients at different deformation stages.After seepage-shear tests,the composition of clay minerals and microscopic structure on the shear surface were analyzed through X-ray and scanning electron microscope(SEM)to understand the coupling effects of seepage on strength.The results revealed that the sliding zone soil exhibited strain-hardening without seepage pressure.However,the introduction of seepage caused a significant reduction in shear strength,resulting in strain-softening characterized by a three-stage process.Long-term seepage action softened clay particles and transported broken particles into effective seepage channels,causing continuous damage to the interior structure and reducing the permeability coefficient.Increased seepage pressure decreased the peak strength by disrupting occlusal and frictional forces between sliding zone soil particles,which carried away more clay particles,contributing to an overhead structure in the soil that raised the permeability coefficient and decreased residual strength.The internal friction angle was less sensitive to variations in seepage pressure than cohesion.
基金State Key Research Development Program of China,Grant/Award Number:2021YFC3001301。
文摘As the first gold mine discovered at the sea in China and the only coastal gold mine currently mined there,Sanshandao Gold Mine faces unique challenges.The mine's safety is under continual threat from its faulted structure coupled with the overlying water.As the mining proceeds deeper,the risk of water inrush increases.The mine's maximum water yield reaches 15000 m3/day,which is attributable to water channels present in fault zones.Predominantly composed of soil–rock mixtures(SRM),these fault zones'seepage characteristics significantly impact water inrush risk.Consequently,investigating the seepage characteristics of SRM is of paramount importance.However,the existing literature mostly concentrates on a single stress state.Therefore,this study examined the characteristics of the permeability coefficient under three distinct stress states:osmotic,osmotic–uniaxial,and osmotic–triaxial pressure.The SRM samples utilized in this study were extracted from in situ fault zones and then reshaped in the laboratory.In addition,the micromechanical properties of the SRM samples were analyzed using computed tomography scanning.The findings reveal that the permeability coefficient is the highest under osmotic pressure and lowest under osmotic–triaxial pressure.The sensitivity coefficient shows a higher value when the rock block percentage ranges between 30%and 40%,but it falls below 1.0 when this percentage exceeds 50%under no confining pressure.Notably,rock block percentages of 40%and 60%represent the two peak points of the sensitivity coefficient under osmotic–triaxial pressure.However,SRM samples with a 40%rock block percentage consistently show the lowest permeability coefficient under all stress states.This study establishes that a power function can model the relationship between the permeability coefficient and osmotic pressure,while its relationship with axial pressure can be described using an exponential function.These insights are invaluable for developing water inrush prevention and control strategies in mining environments.
基金supported by the National Natural Science Foundation of China (Grant Nos.52278334 and 4197724)Fundamental Research Funds for the Central Universities (Grant No.2242024k30066).
文摘It has been well recognized that sand particles significantly affect the mechanical properties of reconstituted sandy clays,including the hosted clay and sand particles.However,interrelation between the permeability and compressibility of reconstituted sandy clays by considering the structural effects of sand particles is still rarely reported.For this,a series of consolidation-permeability coefficient tests were conducted on reconstituted sandy clays with different sand fractions(ψ_(ss)),initial void ratio of hosted clays(e_(c0))and void ratio at liquid limit of hosted clays(e_(cL)).The roles of ψ_(ss) in both the relationships of permeability coefficient of hosted clay(k_(v-hosted clay))versus effective vertical stress(σ'_(v))and void ratio of hosted clay(e_(c-hosted clay))versus σ'_(v) were analyzed.The results show that the permeability coefficient of reconstituted sandy clays(k_(v))is dominated by hosted clay(k_(v)=k_(v-hosted clay)).Both ψ_(ss) and σ'_(v) affect the k_(v) of sandy clays by changing the e_(c-hosted clay) at any given σ'_(v).Due to the partial contacts and densified clay bridges between the sand particles(i.e.structure effects),the e_(c-hosted clay) in sandy clays is higher than that in clays at the same σ'_(v)v.The k_(v)-e_(c-hosted clay) relationship of sandy clays is independent of σ'_(v) and ψ_(ss)but is a function of e_(cL).The types of hosted clays affect the k_(v) of sandy clays by changing the e_(cL).Based on the relationship between permeability coefficient and void ratio for the reconstituted clays,an empirical method for determining the k_(v) is proposed and validated for sandy clays.The predicted values are almost consistent with the measured values with k_(v-predicted)=k_(v-measured)=0.6-2.5.
基金the National Natural Science Foundation of China (Nos. 42302143, 42172159)China Geological Survey Project (No. DD20211350)support from the G. Albert Shoemaker endowment
文摘Clayey-silt natural gas hydrate reservoirs in the South China Sea exhibit loose and unconsolidated structures, heterogeneous pore structures, high clay mineral contents, and strong hydrophilicity. These characteristics complicate the gas-water two-phase flow process in porous media following hydrate decomposition, posing challenges for efficient development. This study examines the transport response of clayey-silt reservoir samples from the Shenhu area using gas-water two-phase flow experiments and CT scanning to explore changes in pore structure, gas-water distribution, and relative permeability under varying flow conditions. The results indicate that pore heterogeneity significantly influences flow characteristics. Gas preferentially displaces water in larger pores, forming fracture-like pores, which serve as preferential flow channels for gas migration. The preferential flow channels enhance gas-phase permeability up to 19 times that of the water phase when fluid pressures exceed total stresses. However,small pores retain liquid, leading to a high residual water saturation of 0.561. CT imaging reveals that these hydro-fractures improve gas permeability but also confine gas flow to specific channels. Pore network analysis shows that gas injection expands the pore-throat network, enhancing connectivity and forming fracture-like pores. Residual water remains trapped in smaller pores and throats, while structural changes, including new fractures, improve gas flow pathways and overall connectivity. Relative permeability curves demonstrate a narrow gas-water cocurrent-flow zone, a right-shifted iso-permeability point and high reservoir capillary pressure, indicating a strong "water-blocking" effect. The findings suggest that optimizing reservoir stimulation techniques to enhance fracture formation, reduce residual water saturation, and improve gas flow capacity is critical for efficient hydrate reservoir development.
基金funded by the joint fund of the National Key Research and Development Program of China(Grant No.2021YFC2902101)National Natural Science Foundation of China(Grant No.52374084)+1 种基金the 111 Project(Grant No.B17009)DE acknowledges support from the G.Albert Shoemaker endowment.
文摘Understanding the relationship between normal stiffness and permeability in rock fractures under high and true-triaxial in situ stress conditions is critical to assess hydro-mechanical coupling in the Earth's crust.Previous data on stiffness–permeability relations are measured under uniaxial stress states as well as under normal stress.However,many projects involve faulted formations with complex three-dimensional(3D)stress states or significant changes to the original stress state.We rectified this by following the permeability evolution using a true-triaxial stress-permeability apparatus as well as independently applying a spectrum of triaxial stresses from low to high.The relationship between permeability and fracture normal stiffness was quantified using constraints based on the principle of virtual work.The impacts of fracture-lateral and fracture-normal stresses on permeability and normal stiffness evolution were measured.It was found that permeability decreases with increasing fracture-lateral and fracture-normal stresses as a result of Poisson confinement,independent of the orientation of the fracture relative to the stresses.The lateral stresses dominated the evolution of normal stiffness at lower normal stresses(σ_(3)=10 MPa)and played a supplementary role at higher normal stresses(σ_(3)>10 MPa).Moreover,correlations between the evolution of permeability and normal stiffness were extended beyond the low-stiffness,high-permeability region to the high-stiffness,low-permeability region under high fracture-lateral stresses(10–80 MPa)with fracture-normal stress(10–50 MPa)conditions.Again,high lateral stresses further confined the fracture and therefore reduced permeability and increased normal stiffness,which exceeded the previous reported stiffness under no lateral stress conditions.This process enabled us to identify a fundamental change in the flow regime from multi-channel to isolated channelized flow.These results provide important characterizations of fracture permeability in the deep crust,including recovery from deep shale-gas reservoirs.
基金supported by the National Natural Science Foundation of China(Grant No.52409132)China Postdoctoral Science Foundation(Grant No.2024M751813)the Major key technical research projects of Shandong Energy Group(Grant No.SNKJ2023A07-R14).
文摘The structural integrity of the interface between a concrete plug and the surrounding rock may be compromised during frequent cycles of air charging,discharging,and storage,which is typical of compressed air energy storage systems in abandoned mines.To investigate this,nitrogen permeability tests were conducted on the interface samples of rockeconcrete interface in both consolidated and unconsolidated states under cyclic loading.The variations in the flow rate throughout the permeability process under different cycle numbers and load range conditions were investigated.The microscopic analysis at the interfaces was imaged using computed tomography scanning.The results indicated that the gas permeability of the cemented interfaces with different roughness values varied with confining pressure ranging from 10^(-13) m^(2) to 10^(-12) m^(2),whereas that of the non-cemented interfaces ranged from 10^(-12) m^(2) to 10^(-11) m^(2).A larger load variation range encompassed the permeability variation characteristics within a smaller variation range.The evolution pattern of the permeability ratio with the number of cycles was influenced by the inlet pressure.The greater the inlet pressure,the larger the increment ratio of the permeability.The permeability change patterns of interfaces with different roughness values were similar.Microscopic analysis revealed that pores inside the concrete were connected to the interface gaps.Under the coupling of stress and gas pressure,the gas could penetrate the crack tips or pores,accelerating the development of microcracks during the cyclic opening and closing of the pores.This study provides valuable insights into the safe long-term operation of underground high-pressure air storage.
基金supported by the Projection of State Key Laboratory of Environment-friendly Energy Materials,Southwest University of Science and Technology(20FKSY23)。
文摘Phenolic resin-based porous composites are the promising thermal protection materials for aerospace applications.The high-temperature evolution of microstructure due to the decomposition of the resin also presents great challenges to predict the internal heat and mass transport behaviors.This work investigates the effects of microstructural characteristics such as the number of pores,size distribution,pore-throats size and volume fraction on the permeation behaviors of fluid in the needle-punched short-cut fiber reinforced silicon phenolic resin-based porous composites.The specimens are prepared by the sol-gel method and the atmospheric pressure drying process and the pyrolysis experiment are conducted at 400℃and 800℃.Then,a scanning electron microscope and a Nano-CT computer tomography are applied to obtain the surface morphologies and the interior slice images of the specimens.The AVIZO software is employed to accurately extract and analyze the pore structural model and simulated calculate the absolute permeability.It is found that the small pores develop gradually during pyrolysis due to the resin decomposition and the quartz fibers rearrangement,resulting in an increase in number of large pores.Nonetheless,the equivalent radii of most pores are less than 1μm.Very few pores possess a large radius over 5μm.However,the volume fraction of these large pores exceeds 99%.In addition,with the pore size growing,the connectivity between these pores is enhanced,immediately causing an increase in number and size of the pore-throats.Larger pore and more pore-throats would add the unblocked flow channels for the fluid passing,reducing flow resistance.The seepage simulation also confirms that the absolute permeability gains significant increase after pyrolysis in all directions.For example,the absolute permeability of the pyrolyzed sample is 9.0×10^(-13)m^(2) in X direction,which is an order of magnitude greater than that of the unpyrolyzed sample.This study provides important insights for understanding the high-temperature evolution at of microstructure and the permeation behavior of fluid in porous thermal protection materials.
基金supported by the China Postdoctoral Science Foundation Funded Project(Grant No.2023M740385)the Postdoctoral Fellowship Program of CPSF(Grant No.GZC20233326)the support by the Helmholtz Association's Initiative and Networking Fund for the Helmholtz Young Investigator Group ARES(Contract No.VH-NG-1516).
文摘In subsurface projects where the host rock is of low permeability,fractures play an important role in fluid circulation.Both the geometrical and mechanical properties of the fracture are relevant to the permeability of the fracture.To evaluate this relationship,we numerically generated self-affine fractures reproducing the scaling relationship of the power spectral density(PSD)of the measured fracture surfaces.The fractures were then subjected to a uniform and stepwise increase in normal stress.A fast Fourier transform(FFT)-based elastic contact model was used to simulate the fracture closure.The evolution of fracture contact area,fracture closure,and fracture normal stiffness were determined throughout the whole process.In addition,the fracture permeability at each step was calculated by the local cubic law(LCL).The influences of roughness exponent and correlation length on the fracture hydraulic and mechanical behaviors were investigated.Based on the power law of normal stiffness versus normal stress,the corrected cubic law and the linear relationship between fracture closure and mechanical aperture were obtained from numerical modeling of a set of fractures.Then,we derived a fracture normal stiffness-permeability equation which incorporates fracture geometric parameters such as the root-mean-square(RMS),roughness exponent,and correlation length,which can describe the fracture flow under an effective medium regime and a percolation regime.Finally,we interpreted the flow transition behavior from the effective medium regime to the percolation regime during fracture closure with the established stiffness-permeability function.
基金Funded by the National Natural Science Foundation of China project(Nos.52108219 and U21A20150)the Lanzhou University of Technology Hongliu Outstanding Young Talent Program,China(No.04-062407)the Research on Quality Control Technology of High-performance Concrete Prepared by Manufactured Sand(No.2020Y21)。
文摘In view of the increased focus on“green”and sustainable development and compliance with the national strategy for“carbon peak and carbon neutrality,”this study investigated the effect of replacing cement(0-20%)with limestone powder(stone powder)as a mineral admixture on the micro,meso,and macro properties of mortar.First,the applicability of stone powder was examined based on the physical filling and heat of hydration of stone powder-cement.Second,micro-meso testing methods,such as X-ray diffraction,scanning electron microscopy,thermogravimetry-differential scanning calorimetry,and nuclear magnetic resonance,were utilized to reveal the influencing mechanisms of stone powder on the microstructure of the mortar.Furthermore,the effect of stone powder on the compressive strength and gas permeability of the mortar was analyzed.Additionally,the time-dependent variations in the gas permeability and its functional relationship with the mechanical properties were determined.Finally,the correlation between the compressive strength and gas permeability with respect to the pore size of stone powder-doped mortar was established via gray-correlation analysis.The results show that an appropriate amount of stone powder(5%)can effectively improve the particle gradation,decelerate the release of the heat of hydration,increase the amount of hydration products,and improve the pore structure,thereby increasing the compressive strength and reducing the gas permeability coefficient.The gas permeability of stone powder-doped mortar was found to exhibit good time-dependent characteristics as well as a quadratic linear correlation with the compressive strength.The gray-correlation analysis results indicate that air pores exhibit the highest influence on the compressive strength and that the gas permeability coefficient is most significantly affected by large pores.
